A two-phase, multicomponent model has been developed for liquidfeed direct methanol fuel cells (DMFC). Diffusion and convection of both gas and liquid phases are considered in the backing layer and flow channel as well as the anode and cathode electrochemical reactions. In particular, the model fully accounts for the mixed potential effects of methanol oxidation at the cathode as a result of methanol crossover caused by diffusion, convection and electro-osmosis. The comprehensive model is

more »

... numerically using computational fluid dynamics (CFD). The transport phenomena and electrochemical kinetics in a liquid-feed DMFC are discussed in detail and the effects of methanol concentration in the anode feed on cell performance are explored. The model is validated against limited DMFC experimental data with reasonable agreement. It is found that the void fraction at the anode outlet is as high as 90% at the cell current density of 0.7A/cm 2 for a 7cm long channel. The increase in methanol feed concentration leads to a slight decrease in cell voltage and a proportional increase in the mass-transport limiting current density for the methanol concentration below 1M. The cell voltage, however, is greatly reduced by excessive methanol crossover and the maximum current density begins to be limited by oxygen supply at the cathode when the methanol feed concentration is larger than 2M under the operating conditions considered. The oxygen depletion results from excessive parasitic oxygen consumption by methanol crossed over.